Curious fossil clusters found beneath the North Sea could be the remains of meals vomited by plesiosaurs around 160 million years ago.
The discovery comes from cores taken from underwater rocks off the coast of Norway. These long cylinders of rock make it possible to read the ancient layers crossed during drilling. Several contained very dense clusters of small fossil remains.
Statue of a plesiosaur in the United States.
Image Wikimedia
Inside, researcher Dirk Knaust identified bivalve shells, tubes produced by marine worms, crinoid remains and a few plant fragments. Some elements were intact, while others were broken or attacked. Their concentration over just a few centimeters did not match an ordinary accumulation caused by waves.
One explanation fits the evidence better: these elements may have remained in an animal's digestive system before being expelled through its mouth. Such fossilized remains are called regurgitalites. Here, some clusters exceeded 10 cm, implying an animal of considerable size.
Who could have produced them? Several predators lived in these Jurassic seas. Ancient sharks remain a possibility, but the study focuses mainly on long-necked plesiosaurs from the cryptoclidid family. Some adults measured several meters and could feed on animals living on or in the seafloor.
The location where the clusters were found provides an additional clue. They occur mostly in ancient deposits near deltas, subject to the arrival of freshwater. Yet some animals contained in these expulsions lived in distinctly marine water. The predator would therefore have eaten farther offshore before moving closer to the coast.
This movement could reflect a repeated habit: searching for prey on the seafloor, then expelling indigestible parts near the shore. Modern animals, particularly some marine mammals, can also regurgitate food remains. The identity of the producer nevertheless remains an interpretation, not direct proof.
These clusters subsequently met different fates. Some were dispersed by burrowing organisms, while others were moved by currents or hardened in the rock. Recognizing them in other cores could now reveal traces of animal behavior that had until now been mistaken for simple concentrations of shells.